In the field of interventional radiology, procedures such as biopsies or punctures are performed in combination with an imaging device which provides guidance during the biopsy procedure to a region of interest for the tissue sample. Magnetic Resonance (MR) scanners are useful imaging devices in this context: the radiologist and the patient are not exposed to any ionizing radiation, and the images provided by MR scanners provide a high level of contrast and sufficient resolution to identify small structures such as early stage tumors.
One of the factors limiting the accuracy of such guided biopsy techniques is needle deflection during the needle insertion. The control of the needle path, previously achieved with a rigid needle body assumption, thus evolved towards needle steering by including needle-tissue interaction models, to predict the behavior of the needle from its geometry and tissue modeling. In one prior art system, the needle is simply rotated by 180° when the estimated deflection reaches a given threshold. More complex control strategies have subsequently been developed to compensate for needle deflections and even to avoid anatomical obstacles. In another prior art system, the needle is manipulated from its base, outside the patient body, using a robotic system to create forces and moments on the needle in a similar way to the approach used by clinicians. The stiffness of the tissues at the entry point may limit such a steering strategy, and a robotic system relying on this technique would require mobility in addition to those required for needle insertion and rotation about the needle long axis.
In another prior art device, relative displacements between concentric needles, or a pre-bent needle integrated into a straight cannula, are used to generate a needle trajectory.
The design of an active needle has long been considered of interest, but a primary difficulty for guided use is MR compatibility, due to the interaction between the needle and the magnetic field and RF fields generated by the MR scanner. For example, one prior art system uses a needle with a magnetized compliant section near the tip that is controlled by an external magnetic force, which is not MR-compatible. The thin tip also makes the needle susceptible to buckling. Another prior system utilizes a piezoelectric material deposited on the needle to create a continuous bending effect along the needle. However, this design is not optimized for steering the needle tip during insertion. Another prior art system uses a tendon-driven steerable needle, and has been used for lung biopsy procedures, where tissues are much less dense than in the prostate.
The principle of an active needle can also be related to active catheters for navigation in blood vessels, however this type of design cannot be directly exploited for an active needle because of the very different mechanical interactions that exist between a needle and tissues, as compared to the controlled movement of a catheter which is guided by vessel walls.
MR-compatible actuation technologies have also been developed for robotic devices. Pneumatic or hydraulic actuation systems are of interest, the latter presenting an impressive power/volume ratio. However, integrating such technologies in a 1-2 mm diameter needle has not been possible and specific new risks to the patient are presented by the introduction of these methods in a needle biopsy requiring a higher level of active guidance and steering.
It is desired to provide an MR compatible needle which is steerable through a combination of needle deflection and rotation about the needle long axis during and throughout the needle insertion process and provide guidance to a biopsy site.